1. Field of the Invention
The present invention is related to the field of heat exchanger systems and, more particularly, to a heat exchanger of the fin-tube block type, and having improved brazing characteristics for use with extruded tubes.
2. Description of the Related Art
Prior art plate-finned style heat exchangers are known from U.S. Pat. Nos. 4,276,927, 4,473,111 and 4,729,428, among others. Such heat exchangers are characterized by a first set of parallel flow passages extending in one direction and alternating with a second, generally perpendicularly-oriented, arrangement of flow passages, the first and second sets being separated by a plate and the sequence of components being repeated to form a multi-layer sandwich core. A first fluid is directed through the first set of flow passages, while a second fluid passes through the second set of flow passages, with heat being exchanged therebetween. Generally the shape, spacing, and orientation of the first set of flow passages, which are defined by spacers interposed between pairs of flat plates, differs somewhat from that of the second set of flow passages, which are generally defined by corrugated or serpentine fins interposed between the plate-spacer layers.
Depending on the construction of the two sets of flow passages, difficulties arise when effecting the necessary bonding of the components to create the sandwich-type core. The flow passages arranged in one direction must be bonded to the flow passages or fins extending in the other. This may be accomplished through the use of header bars and end pieces as is shown in U.S. Pat. Nos. 4,473,111 and 6,019,169. Problems are often encountered due to the limited surface area of the bonding surfaces. Increased bonding surface, as well as increased strength, may be provided through thickened end or side walls, as taught in U.S. Pat. No. 4,729,428.
The prior art plate-finned type heat exchangers require numerous individual components, and therefore present numerous potential leak paths. This problem can be alleviated through the use of extruded tubes in place of the plate-spacer layers, as taught by U.S. Pat. No. 6,019,169. However, the use of extrusions presents other problems, particularly when the heat exchanger core components are made of aluminum.
In the prior art plate-finned type heat exchangers, brazed aluminum cores clad a low temperature-melting alloy onto the material of one or more of the components in order to bond the assembly together during the brazing process. Extrusions do not lend themselves to cladding. Therefore the braze material for bonding the tube to the fin can be provided by either applying powdered braze material in a binder to the tubes, or by cladding a low temperature melting alloy to the fin material. However, the application of powdered braze material in a binder to the tube does not provide enough braze material to consistently bond the tube to the header bar.
Accordingly, a need exists for a fin-tube block type heat exchanger construction capable of effectively and consistently bonding extruded tubes to corresponding header bars.